Collecting apparatuses of this type are disclosed, for example, in EP 1 471 022 A1 and EP 1 857 390 A1. These known collecting apparatuses have a collecting drum which can be driven in rotation, to which the sheets which are to be processed are fed by means of a feeding device and on which the sheets, which are fed one behind the other, are secured temporarily and collected to form sheet stacks. The sheets are secured on the circumference of the collecting drums by mechanical securing devices or by means of electrostatic forces of attraction. In order for it to be possible to process sheets of different formats, i.e. of different format lengths, the circumferential speed of the collecting drum and/or the feeding speed of the feeding device has to be altered and adapted to the varying format lengths. This requires corresponding outlay in terms of regulating equipment.